1. Field of the Invention
The present invention relates to a method of purifying 1,3-bis(aminomethyl)cyclohexane (1,3-BAC) by distillation, more specifically, relates to a method of purifying 1,3-BAC which includes a step of distilling a crude liquid containing 1,3-BAC to remove a high-boiling component having a boiling point higher than that of 1,3-BAC thereby to obtain a purified 1,3-BAC. 1,3-BAC is a useful compound that has been widely used in industrial applications such as resin curing agents, raw materials for polyamide, raw materials for isocyanate, rubber chemicals, paper processing agents, fiber treating agents and cleaning agents.
2. Description of the Prior Art
As the production methods of 1,3-BAC, there are known a method of hydrogenating the benzene ring of m-xylylenediamine (JP 42-26783B, JP 50-126638A, JP 51-7659B, JP 54-16452A and JP 8-143514A), a method of simultaneously hydrogenating the benzene ring and nitrile group by the reaction of isophthalonitrile and hydrogen (JP 51-68540A and JP 10-76160A), a method of hydrogenating dicyanocyclohexane (Japanese Patent No. 2718740, JP 41-21338B and JP 2001-187765 A), etc.
As to the purification by distillation of a crude reaction product liquid containing 1,3-BAC obtained in the methods described above, JP 49-42645A teaches that the production of low boiling compounds such as methylene cyclohexylmethylamine can be avoided by coexisting nitrogen, ammonia or water during maintaining 1,3-BAC under heating conditions.
In the method taught by JP 49-42645A where water is coexisted, the water should be finally removed to obtain a high purity 1,3-BAC. If ammonia is coexisted, the ammonia is dissolved in the distilled 1,3-BAC to generate pungent odor. When nitrogen is coexisted, the nitrogen introduced into the 1,3-BAC-containing liquid placed at the column bottom is finally exhausted into a vacuum line after passing through the internal portion of distillation column and column top. Therefore, the vapor load in the inside of column is increased to reduce the treating capacity of distillation column. Also, the vacuum apparatus with higher capacity is needed because the load of vacuum line is increased. In addition, the loss of 1,3-BAC is increased because 1,3-BAC accompanies with nitrogen to escape into the vacuum line.
The inventors have conducted the distillation of a 1,3-BAC-containing liquid according to the method taught by JP 49-42645A. The results of distillation varied depending on the starting liquid to be distilled and the distillation conditions. In some cases, a large amount of low-boiling components were generated by the degradation of 1,3-BAC, and the generated low-boiling components contaminated the distilled 1,3-BAC. Thus, the method proposed by JP 49-42645A failed to sufficiently prevent the decomposition of 1,3-BAC.